mm/balloon_compaction: remove balloon mapping and flag AS_BALLOON_MAP

Now ballooned pages are detected using PageBalloon().  Fake mapping is no
longer required.  This patch links ballooned pages to balloon device using
field page->private instead of page->mapping.  Also this patch embeds
balloon_dev_info directly into struct virtio_balloon.

Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@samsung.com>
Cc: Rafael Aquini <aquini@redhat.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 39 insertions, 206 deletions

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index c3eb93fc9261..2bad7f9dd2ac 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -59,7 +59,7 @@ struct virtio_balloon
          * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
          * to num_pages above.
          */
-        struct balloon_dev_info *vb_dev_info;
+        struct balloon_dev_info vb_dev_info;
 
         /* Synchronize access/update to this struct virtio_balloon elements */
         struct mutex balloon_lock;
@@ -127,7 +127,7 @@ static void set_page_pfns(u32 pfns[], struct page *page)
 
 static void fill_balloon(struct virtio_balloon *vb, size_t num)
 {
-        struct balloon_dev_info *vb_dev_info = vb->vb_dev_info;
+        struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
 
         /* We can only do one array worth at a time. */
         num = min(num, ARRAY_SIZE(vb->pfns));
@@ -171,7 +171,7 @@ static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
 static void leak_balloon(struct virtio_balloon *vb, size_t num)
 {
         struct page *page;
-        struct balloon_dev_info *vb_dev_info = vb->vb_dev_info;
+        struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
 
         /* We can only do one array worth at a time. */
         num = min(num, ARRAY_SIZE(vb->pfns));
@@ -353,12 +353,11 @@ static int init_vqs(struct virtio_balloon *vb)
         return 0;
 }
 
-static const struct address_space_operations virtio_balloon_aops;
 #ifdef CONFIG_BALLOON_COMPACTION
 /*
  * virtballoon_migratepage - perform the balloon page migration on behalf of
  *                           a compation thread.     (called under page lock)
- * @mapping: the page->mapping which will be assigned to the new migrated page.
+ * @vb_dev_info: the balloon device
  * @newpage: page that will replace the isolated page after migration finishes.
  * @page   : the isolated (old) page that is about to be migrated to newpage.
  * @mode   : compaction mode -- not used for balloon page migration.
@@ -373,17 +372,13 @@ static const struct address_space_operations virtio_balloon_aops;
  * This function preforms the balloon page migration task.
  * Called through balloon_mapping->a_ops->migratepage
  */
-static int virtballoon_migratepage(struct address_space *mapping,
+static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
                 struct page *newpage, struct page *page, enum migrate_mode mode)
 {
-        struct balloon_dev_info *vb_dev_info = balloon_page_device(page);
-        struct virtio_balloon *vb;
+        struct virtio_balloon *vb = container_of(vb_dev_info,
+                        struct virtio_balloon, vb_dev_info);
         unsigned long flags;
 
-        BUG_ON(!vb_dev_info);
-
-        vb = vb_dev_info->balloon_device;
-
         /*
          * In order to avoid lock contention while migrating pages concurrently
          * to leak_balloon() or fill_balloon() we just give up the balloon_lock
@@ -399,7 +394,7 @@ static int virtballoon_migratepage(struct address_space *mapping,
 
         /* balloon's page migration 1st step  -- inflate "newpage" */
         spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
-        balloon_page_insert(newpage, mapping, &vb_dev_info->pages);
+        balloon_page_insert(vb_dev_info, newpage);
         vb_dev_info->isolated_pages--;
         spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
         vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
@@ -418,18 +413,11 @@ static int virtballoon_migratepage(struct address_space *mapping,
 
         return MIGRATEPAGE_SUCCESS;
 }
-
-/* define the balloon_mapping->a_ops callback to allow balloon page migration */
-static const struct address_space_operations virtio_balloon_aops = {
-                        .migratepage = virtballoon_migratepage,
-};
 #endif /* CONFIG_BALLOON_COMPACTION */
 
 static int virtballoon_probe(struct virtio_device *vdev)
 {
         struct virtio_balloon *vb;
-        struct address_space *vb_mapping;
-        struct balloon_dev_info *vb_devinfo;
         int err;
 
         vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
@@ -445,30 +433,14 @@ static int virtballoon_probe(struct virtio_device *vdev)
         vb->vdev = vdev;
         vb->need_stats_update = 0;
 
-        vb_devinfo = balloon_devinfo_alloc(vb);
-        if (IS_ERR(vb_devinfo)) {
-                err = PTR_ERR(vb_devinfo);
-                goto out_free_vb;
-        }
-
-        vb_mapping = balloon_mapping_alloc(vb_devinfo,
-                                           (balloon_compaction_check()) ?
-                                           &virtio_balloon_aops : NULL);
-        if (IS_ERR(vb_mapping)) {
-                /*
-                 * IS_ERR(vb_mapping) && PTR_ERR(vb_mapping) == -EOPNOTSUPP
-                 * This means !CONFIG_BALLOON_COMPACTION, otherwise we get off.
-                 */
-                err = PTR_ERR(vb_mapping);
-                if (err != -EOPNOTSUPP)
-                        goto out_free_vb_devinfo;
-        }
-
-        vb->vb_dev_info = vb_devinfo;
+        balloon_devinfo_init(&vb->vb_dev_info);
+#ifdef CONFIG_BALLOON_COMPACTION
+        vb->vb_dev_info.migratepage = virtballoon_migratepage;
+#endif
 
         err = init_vqs(vb);
         if (err)
-                goto out_free_vb_mapping;
+                goto out_free_vb;
 
         vb->thread = kthread_run(balloon, vb, "vballoon");
         if (IS_ERR(vb->thread)) {
@@ -480,10 +452,6 @@ static int virtballoon_probe(struct virtio_device *vdev)
 
 out_del_vqs:
         vdev->config->del_vqs(vdev);
-out_free_vb_mapping:
-        balloon_mapping_free(vb_mapping);
-out_free_vb_devinfo:
-        balloon_devinfo_free(vb_devinfo);
 out_free_vb:
         kfree(vb);
 out:
@@ -509,8 +477,6 @@ static void virtballoon_remove(struct virtio_device *vdev)
 
         kthread_stop(vb->thread);
         remove_common(vb);
-        balloon_mapping_free(vb->vb_dev_info->mapping);
-        balloon_devinfo_free(vb->vb_dev_info);
         kfree(vb);
 }
 
diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
index 38aa07d5b81c..bc3d2985cc9a 100644
--- a/include/linux/balloon_compaction.h
+++ b/include/linux/balloon_compaction.h
@@ -57,21 +57,22 @@
  * balloon driver as a page book-keeper for its registered balloon devices.
  */
 struct balloon_dev_info {
-        void *balloon_device;           /* balloon device descriptor */
-        struct address_space *mapping;  /* balloon special page->mapping */
         unsigned long isolated_pages;   /* # of isolated pages for migration */
         spinlock_t pages_lock;          /* Protection to pages list */
         struct list_head pages;         /* Pages enqueued & handled to Host */
+        int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
+                        struct page *page, enum migrate_mode mode);
 };
 
 extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
 extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
-extern struct balloon_dev_info *balloon_devinfo_alloc(
-                                                void *balloon_dev_descriptor);
 
-static inline void balloon_devinfo_free(struct balloon_dev_info *b_dev_info)
+static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
 {
-        kfree(b_dev_info);
+        balloon->isolated_pages = 0;
+        spin_lock_init(&balloon->pages_lock);
+        INIT_LIST_HEAD(&balloon->pages);
+        balloon->migratepage = NULL;
 }
 
 #ifdef CONFIG_BALLOON_COMPACTION
@@ -79,14 +80,6 @@ extern bool balloon_page_isolate(struct page *page);
 extern void balloon_page_putback(struct page *page);
 extern int balloon_page_migrate(struct page *newpage,
                                 struct page *page, enum migrate_mode mode);
-extern struct address_space
-*balloon_mapping_alloc(struct balloon_dev_info *b_dev_info,
-                        const struct address_space_operations *a_ops);
-
-static inline void balloon_mapping_free(struct address_space *balloon_mapping)
-{
-        kfree(balloon_mapping);
-}
 
 /*
  * __is_movable_balloon_page - helper to perform @page PageBalloon tests
@@ -120,27 +113,25 @@ static inline bool isolated_balloon_page(struct page *page)
 
 /*
  * balloon_page_insert - insert a page into the balloon's page list and make
- *                       the page->mapping assignment accordingly.
+ *                       the page->private assignment accordingly.
+ * @balloon : pointer to balloon device
  * @page    : page to be assigned as a 'balloon page'
- * @mapping : allocated special 'balloon_mapping'
- * @head    : balloon's device page list head
  *
  * Caller must ensure the page is locked and the spin_lock protecting balloon
  * pages list is held before inserting a page into the balloon device.
  */
-static inline void balloon_page_insert(struct page *page,
-                                       struct address_space *mapping,
-                                       struct list_head *head)
+static inline void balloon_page_insert(struct balloon_dev_info *balloon,
+                                       struct page *page)
 {
         __SetPageBalloon(page);
         SetPagePrivate(page);
-        page->mapping = mapping;
-        list_add(&page->lru, head);
+        set_page_private(page, (unsigned long)balloon);
+        list_add(&page->lru, &balloon->pages);
 }
 
 /*
  * balloon_page_delete - delete a page from balloon's page list and clear
- *                       the page->mapping assignement accordingly.
+ *                       the page->private assignement accordingly.
  * @page    : page to be released from balloon's page list
  *
  * Caller must ensure the page is locked and the spin_lock protecting balloon
@@ -149,7 +140,7 @@ static inline void balloon_page_insert(struct page *page,
 static inline void balloon_page_delete(struct page *page)
 {
         __ClearPageBalloon(page);
-        page->mapping = NULL;
+        set_page_private(page, 0);
         if (PagePrivate(page)) {
                 ClearPagePrivate(page);
                 list_del(&page->lru);
@@ -162,11 +153,7 @@ static inline void balloon_page_delete(struct page *page)
  */
 static inline struct balloon_dev_info *balloon_page_device(struct page *page)
 {
-        struct address_space *mapping = page->mapping;
-        if (likely(mapping))
-                return mapping->private_data;
-
-        return NULL;
+        return (struct balloon_dev_info *)page_private(page);
 }
 
 static inline gfp_t balloon_mapping_gfp_mask(void)
@@ -174,29 +161,12 @@ static inline gfp_t balloon_mapping_gfp_mask(void)
         return GFP_HIGHUSER_MOVABLE;
 }
 
-static inline bool balloon_compaction_check(void)
-{
-        return true;
-}
-
 #else /* !CONFIG_BALLOON_COMPACTION */
 
-static inline void *balloon_mapping_alloc(void *balloon_device,
-                                const struct address_space_operations *a_ops)
+static inline void balloon_page_insert(struct balloon_dev_info *balloon,
+                                       struct page *page)
 {
-        return ERR_PTR(-EOPNOTSUPP);
-}
-
-static inline void balloon_mapping_free(struct address_space *balloon_mapping)
-{
-        return;
-}
-
-static inline void balloon_page_insert(struct page *page,
-                                       struct address_space *mapping,
-                                       struct list_head *head)
-{
-        list_add(&page->lru, head);
+        list_add(&page->lru, &balloon->pages);
 }
 
 static inline void balloon_page_delete(struct page *page)
@@ -240,9 +210,5 @@ static inline gfp_t balloon_mapping_gfp_mask(void)
         return GFP_HIGHUSER;
 }
 
-static inline bool balloon_compaction_check(void)
-{
-        return false;
-}
 #endif /* CONFIG_BALLOON_COMPACTION */
 #endif /* _LINUX_BALLOON_COMPACTION_H */
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 19191d39c4f3..7ea069cd3257 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -24,8 +24,7 @@ enum mapping_flags {
         AS_ENOSPC       = __GFP_BITS_SHIFT + 1, /* ENOSPC on async write */
         AS_MM_ALL_LOCKS = __GFP_BITS_SHIFT + 2, /* under mm_take_all_locks() */
         AS_UNEVICTABLE  = __GFP_BITS_SHIFT + 3, /* e.g., ramdisk, SHM_LOCK */
-        AS_BALLOON_MAP  = __GFP_BITS_SHIFT + 4, /* balloon page special map */
-        AS_EXITING      = __GFP_BITS_SHIFT + 5, /* final truncate in progress */
+        AS_EXITING      = __GFP_BITS_SHIFT + 4, /* final truncate in progress */
 };
 
 static inline void mapping_set_error(struct address_space *mapping, int error)
@@ -55,21 +54,6 @@ static inline int mapping_unevictable(struct address_space *mapping)
         return !!mapping;
 }
 
-static inline void mapping_set_balloon(struct address_space *mapping)
-{
-        set_bit(AS_BALLOON_MAP, &mapping->flags);
-}
-
-static inline void mapping_clear_balloon(struct address_space *mapping)
-{
-        clear_bit(AS_BALLOON_MAP, &mapping->flags);
-}
-
-static inline int mapping_balloon(struct address_space *mapping)
-{
-        return mapping && test_bit(AS_BALLOON_MAP, &mapping->flags);
-}
-
 static inline void mapping_set_exiting(struct address_space *mapping)
 {
         set_bit(AS_EXITING, &mapping->flags);
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 52abeeb3cb9d..3afdabdbc0a4 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -11,32 +11,6 @@
 #include <linux/balloon_compaction.h>
 
 /*
- * balloon_devinfo_alloc - allocates a balloon device information descriptor.
- * @balloon_dev_descriptor: pointer to reference the balloon device which
- *                          this struct balloon_dev_info will be servicing.
- *
- * Driver must call it to properly allocate and initialize an instance of
- * struct balloon_dev_info which will be used to reference a balloon device
- * as well as to keep track of the balloon device page list.
- */
-struct balloon_dev_info *balloon_devinfo_alloc(void *balloon_dev_descriptor)
-{
-        struct balloon_dev_info *b_dev_info;
-        b_dev_info = kmalloc(sizeof(*b_dev_info), GFP_KERNEL);
-        if (!b_dev_info)
-                return ERR_PTR(-ENOMEM);
-
-        b_dev_info->balloon_device = balloon_dev_descriptor;
-        b_dev_info->mapping = NULL;
-        b_dev_info->isolated_pages = 0;
-        spin_lock_init(&b_dev_info->pages_lock);
-        INIT_LIST_HEAD(&b_dev_info->pages);
-
-        return b_dev_info;
-}
-EXPORT_SYMBOL_GPL(balloon_devinfo_alloc);
-
-/*
  * balloon_page_enqueue - allocates a new page and inserts it into the balloon
  *                        page list.
  * @b_dev_info: balloon device decriptor where we will insert a new page to
@@ -61,7 +35,7 @@ struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
          */
         BUG_ON(!trylock_page(page));
         spin_lock_irqsave(&b_dev_info->pages_lock, flags);
-        balloon_page_insert(page, b_dev_info->mapping, &b_dev_info->pages);
+        balloon_page_insert(b_dev_info, page);
         spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
         unlock_page(page);
         return page;
@@ -127,60 +101,10 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
 EXPORT_SYMBOL_GPL(balloon_page_dequeue);
 
 #ifdef CONFIG_BALLOON_COMPACTION
-/*
- * balloon_mapping_alloc - allocates a special ->mapping for ballooned pages.
- * @b_dev_info: holds the balloon device information descriptor.
- * @a_ops: balloon_mapping address_space_operations descriptor.
- *
- * Driver must call it to properly allocate and initialize an instance of
- * struct address_space which will be used as the special page->mapping for
- * balloon device enlisted page instances.
- */
-struct address_space *balloon_mapping_alloc(struct balloon_dev_info *b_dev_info,
-                                const struct address_space_operations *a_ops)
-{
-        struct address_space *mapping;
-
-        mapping = kmalloc(sizeof(*mapping), GFP_KERNEL);
-        if (!mapping)
-                return ERR_PTR(-ENOMEM);
-
-        /*
-         * Give a clean 'zeroed' status to all elements of this special
-         * balloon page->mapping struct address_space instance.
-         */
-        address_space_init_once(mapping);
-
-        /*
-         * Set mapping->flags appropriately, to allow balloon pages
-         * ->mapping identification.
-         */
-        mapping_set_balloon(mapping);
-        mapping_set_gfp_mask(mapping, balloon_mapping_gfp_mask());
-
-        /* balloon's page->mapping->a_ops callback descriptor */
-        mapping->a_ops = a_ops;
-
-        /*
-         * Establish a pointer reference back to the balloon device descriptor
-         * this particular page->mapping will be servicing.
-         * This is used by compaction / migration procedures to identify and
-         * access the balloon device pageset while isolating / migrating pages.
-         *
-         * As some balloon drivers can register multiple balloon devices
-         * for a single guest, this also helps compaction / migration to
-         * properly deal with multiple balloon pagesets, when required.
-         */
-        mapping->private_data = b_dev_info;
-        b_dev_info->mapping = mapping;
-
-        return mapping;
-}
-EXPORT_SYMBOL_GPL(balloon_mapping_alloc);
 
 static inline void __isolate_balloon_page(struct page *page)
 {
-        struct balloon_dev_info *b_dev_info = page->mapping->private_data;
+        struct balloon_dev_info *b_dev_info = balloon_page_device(page);
         unsigned long flags;
 
         spin_lock_irqsave(&b_dev_info->pages_lock, flags);
@@ -192,7 +116,7 @@ static inline void __isolate_balloon_page(struct page *page)
 
 static inline void __putback_balloon_page(struct page *page)
 {
-        struct balloon_dev_info *b_dev_info = page->mapping->private_data;
+        struct balloon_dev_info *b_dev_info = balloon_page_device(page);
         unsigned long flags;
 
         spin_lock_irqsave(&b_dev_info->pages_lock, flags);
@@ -202,12 +126,6 @@ static inline void __putback_balloon_page(struct page *page)
         spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
 }
 
-static inline int __migrate_balloon_page(struct address_space *mapping,
-                struct page *newpage, struct page *page, enum migrate_mode mode)
-{
-        return page->mapping->a_ops->migratepage(mapping, newpage, page, mode);
-}
-
 /* __isolate_lru_page() counterpart for a ballooned page */
 bool balloon_page_isolate(struct page *page)
 {
@@ -274,7 +192,7 @@ void balloon_page_putback(struct page *page)
 int balloon_page_migrate(struct page *newpage,
                          struct page *page, enum migrate_mode mode)
 {
-        struct address_space *mapping;
+        struct balloon_dev_info *balloon = balloon_page_device(page);
         int rc = -EAGAIN;
 
         /*
@@ -290,9 +208,8 @@ int balloon_page_migrate(struct page *newpage,
                 return rc;
         }
 
-        mapping = page->mapping;
-        if (mapping)
-                rc = __migrate_balloon_page(mapping, newpage, page, mode);
+        if (balloon && balloon->migratepage)
+                rc = balloon->migratepage(balloon, newpage, page, mode);
 
         unlock_page(newpage);
         return rc;